I could only ever imagine someone finding Street Fighter difficult if they had never played a Street Fighter game before in their lives. If that's the case all it takes is for you to master a few characters. Just go into the challenges and it teaches you their moves.
Soul Caliber IV though, I downloaded the demo from the PSN when I was bored one day, it wasn't awful, but I'd definitely never buy it. I'm generally not that big into fighting games beyond the big 3. Street Fighter, Tekken, Mortal Kombat.